Treatment and purification of raw water in order to make it suitable for drinking or the treatment of an industrial fluid stream which may be water can be accomplished by a number of methods. The character of a given water stream may lend itself to the use of a particular treatment. Ion-exchange resins are used in water treatment systems in order to remove dissolved compounds, some of which are organic. Microfiltration and Ultrafiltration membranes are used to remove particulates. For a water stream that contains both these components, one treatment must be used, followed by the second. The need for two separate steps is time-consuming, requires additional equipment, and increases the overall cost of the treatment system. Accordingly, there remains a need for an improved water treatment system that can remove particulates and dissolved organic compounds and which is cost- and time-effective compared to present systems.
Benedek, U.S. Pat. No. 6,027,649, discloses the treatment of drinking water in a single reactor tank using a ZEWEED® submerged membrane filter in conjunction with a flocculent mixed in the reactor tank and maintained in suspension by use of an air bubbler. The flocculent is intended to remove organics, color, bacteria, cysts and other impurities. Use of the flocculent taught by Benedek requires maintaining pH in a range from 5–9. This may require addition of acids or bases to a raw water supply to maintain the necessary pH range. While Benedek teaches a single tank using a flocculent in combination with a membrane filter, use of the flocculent for organic removal requires subsequent disposal of the spent flocculent. Thus, not only must suitable disposal for the spent flocculent be arranged, new coagulants must be provided to the reactor tank to form the necessary flocculent. Benedek also discusses the desirability of adding activated carbon to the reactor tank for the removal of dissolved organics. However, as with the flocculent, this creates disposal problems for spent activated carbon and requires replenishment of the reactor tank with new activated carbon.
Daly, U.S. Pat. No. 6,120,688, is directed to a water purification method also utilizing a ZEWEED® membrane filter. More particularly, Daly teaches initial particulate removal using the ZEWEED® filter followed by application of reverse osmosis to the filtered water. While Daly eliminates the disposal problems associated with the flocculent and activated carbon of the Benedek patent, the Daly patent requires a two step treatment process which increases plant size and cost requirements.
The present invention is directed to overcoming one or more of the problems discussed above.